//author:dhclly
const o =console.log;

interface Person {
    firstName: string;
    lastName: string;
}

function greeter(person: Person) {
    return "Hello, " + person.firstName + " " + person.lastName;
}

let user = { firstName: "Jane", lastName: "User" };

o(greeter(user));

interface Point {
    readonly x: number;
    readonly y: number;
}

let a: number[] = [1, 2, 3, 4];
let ro: ReadonlyArray<number> = a;